This invention relates to a process for the intermittent aeration of liquids such as, for instance, waste water or the like media in aeration tanks by means of an aeration device arranged below the surface of the liquid and comprising at least one supporting body, an air-feeding line, and a preferably elastic diaphragm covering the supporting body and being of air-tight material having as perforations punctures, slots or holes in parts thereof, as well as a frame structure locking the supporting body in position.
An air-distributing device for carrying out a process of aeration by treating water with fine air bubbles is known from the German patent No. 29 42 607, the criterion of which is the arrangement of an air-tight foil and a perforated foil superimposed on the former, in a frame constituted by two oppositely directed angle frames which have the function of a tentering frame, with supporting stays extending underneath the unperforated foil being further connected to the said frame. Above the perforated foil, there are provided further, uniformly distributed stabilizing foils at a short distance from the foil, which extend at 90.degree. relative to the lower stays.
A thus devised air distributor will indeed fulfill the tasks confronting it in this instance in so far as a most uniform distribution of air possible can be achieved over the entire distributor surface. This device suffers, however, from the drawback of requiring a relatively heavy, well stiffened, weight-demanding double frame construction which renders manipulation of the aerator in the aeration tank difficult.
A further drawback of this construction is the position of the plane in which the aeration surface lies under the surface of the water, which position depends on the weight and cannot be adjusted.
Furthermore, devices are known which have supporting bodies provided with openings for the passage of air and covered by a perforated air-distributing foil or enveloped by a perforated hose, and which as a rule require the arrangement of additional tensioning means for locking the hoses or foils, respectively, in position.
These known devices suffer generally from the drawback that, in the case of possible damaging of the air distributor foil which can always occur for any number of reasons, water may penetrate into the supporting body and can lead to a premature closing of the perforations, in particular in a period of rest.
Moreover, it is not only the air-distributing foil or perforated hose, respectively, which is endangered by the entering waste water but especially the supporting body itself as the cross sectional areas of the air discharge openings in the supporting body are in such a case openly accessible practically without restriction.
It is a further drawback that, in the case of tubular aerators, only the upper reach can be considered as the aerating region proper, and this region is, in many cases, interrupted by auxiliary holding sleeves or the like.
As in the case of the initially named publication, an attempt is often made to give the aerating foil a position of aeration as nearly horizontal as possible, with the aid of stays keeping it down, in order to avoid excessive tensioning of the upwardly vaulted region thereof.
As a foil displacement underneath the stays cannot be excluded, excessive tensioning may nevertheless occur in the individual supported areas.
The superpositioning of sheet metal sieves which has also been tried, will reduce the uniformity of air distribution.